Automatic electric toaster



July 10, 1951 B. G. OLVING AUTOMATIC ELECTRIC TOASTER 4 Sheets-Sheet 1 Filed March 2, 1945 I N VEN TOR. BR 0/? G. 04 v/kvc July 10, 1951 B. G. OLVlNG 2,560,389

AUTOMATIC ELECTRIC TOASTER Filed March 2, 1945 4 Sheets-Sheet 2 w a L/ t J a July 10, 1951 B. G. OLVING AUTOMATIC ELECTRIC TOASTER Filed March 2, 1945 4 Sheets-Sheet 5 I N VEN TOR BRO/ 6. 0L V/A/G July 10, 1951 oLvING 2,560,389

AUTOMATIC ELECTRIC TOASTER Filed March 2, 1945 4 Sheets-Sheet 4 IN V EN TOR. Y BRO/ 6. UL w/va Patented July 10, 1951 AUTOMATIC ELECTRIC TOASTER Bror G. Olving, Elgin, 111., assignor to McGraw Electric Company; Elgin, 111., a corporation of Delaware Application March 2, 1945, Serial No. 580,675

7 Claims. 1

My invention relates to electric toasters and particularly to timing circuits for such toasters.

An object of my invention is to provide a timing means and an electric circuit therefor which are dependable and will stand up in service for a relatively long time of use.

'Another object of my invention is to provide a timing means, the performanceof Which de pends upon the inherent electrical characteristics of its component parts and the operation of which is not dependent on or controlled by any energy supplied from mechanical or thermal storage devices.

Another object of my invention is to provide a timing mean and an electric circuit therefor including an electron tube to obtain the above-mentioned operation.

Another object of my invention is to provide an electric circuit comprising an electron tube as well as means for charging an electrostatic condenser as soon as a connecting plug is connected across a supply circuit, which condenser shall discharge gradually and cause firing of said electron tube at a predetermined minimum voltage, to cause termination of a toasting operation.

Other objects of my invention will either be apparent from a description of one form of circuit embodying my invention or will be pointed out in the course of such description and set forth particularly in the appended claims.

In the drawings,

Figure 1 is a side elevational view of a toaster embodying my invention,

Fig. 2 is a front elevational View thereof, both Figs. 1 and 2 being shown on a reduced scale,

Fig. 3 is a Vertical, longitudinal, sectional view taken on the line 3-3 of Fig. 4,

Fig. 4 is a vertical, lateral, sectional view taken on the line 4-4 of Fig. 3,

Fig. 5 is a fragmentary, horizontal, sectional view taken on the line 5-5 of Fig. 4,

Fig. 6 is a bottom view of the assembled timer means,

7 Fig.7 is an end view of the parts shown in Fig. 6,

Fig. 8 is a diagram of connections embodyingmy invention,

Fig. 9 is a diagram of connections substantially the same as shown in Fig. 8 except that the parts are shown in the positions they will occupy after start of a toasting operation, and,

- Fig. 10 is a modified diagram of connections embodying the invention.

Referring first of all to Figs. 1 to 7 inclusive, I have there shown a domestic two-slice toaster designated by numeral l I which comprises abase 2 frame ['3 which may be made of molded compositionin'aterial and which has positioned thereon a bottom plate 15 as well as an outer casing I! which has a cover member l9 thereon.

I provide also pairs of electric toast heating elements 2| which extend substantially Vertically from the bottom plate l5. Each element 2| comprises one or more sheets 23 of thin electric-insulating material, such as mica, on which is wound a strip or strand 25 of suitable electric-resistance material. I provide also a plurality of vertical guard or guide wires 2? which may be suspended from horizontally extending frame plates 29 supported adjacent the upper end of the outer casing I1.

I provide also bread carriers 3| positioned in each of the toasting chambers which are constituted by one of the inner toast heating elements 2| as well as an outer bafile plate 33. I provide also a rear intermediate wall 35 as well as a front intermediate wall 31, the front and rear intermediate walls cooperating with the inner toast heating element 2| and the outer baflle plate to provide a toasting chamber.

Since it is desired that the bread carriers shall be vertically movable in their respective toasting chambers from their upper non-toasting position to a lower toasting position and that they shall be normally yieldingly biased into their upper non-toasting position, I provide a tension coil spring 39 having its upper end secured to a bracket 4! which is secured against the front surface of the front intermediate wall 31. The lower end of tension coil 39 is secured to a lug 43 constituting a part of a rear carriage plate 45. I provide a front carriage plate 41 and space it apart from the rear carriage plate as by a plurality of headed studs 49, and on each of the four studs, I mount an externally grooved roller 5l. The studs 49 are positioned adjacent the four corners of the substantially rectangularly shaped rear and front carriage plates and 41. The grooved rollers 5! are adapted to engage the inner surfaces of vertically extending rods 53 and55, the lower ends of which are secured to plate l5 while the upper ends thereof interfit with the front end portions of the top frame plates 29, a cross bar 5'! being provided to hold the front end portions of the top frame plates 29 in proper and desired operative positions. It is to be understood that the rear end portions of the bread carriers 3i extend through vertical slots in the rear intermediate wall 35 while their front end p'ortions extend through vertical slots in the front intermediate wall 31 and are secured to rearwardly extending lugs 59 of the rear carriage plate 45. The provision of the spring 39, therefore, normally yieldingly biases the bread carriers into their upper or non-toasting position from which position they will be moved downwardly into their lowermost or toasting positions by means of a knob 3l' secured on the front outer end portion of a bar 53 which is secured against the front surface of the front carriage plate 41. All of the parts hereinbeiore described are old and well known in the art and constitute no part of my present invention.

Means for holding the bread carriers in their lowermost or non-toasting position after they have been moved into said position in the man ner hereinbefore described, comprises a hook member 65 which is secured on the bottom end portion of a resilient bar 61, the upper end of which is secured against a forwardly extending lug 59 positioned adjacent the right hand upper end portion of front carriage plate 4'? as seen in Fig. 4 of the drawings. The spring bar 51 is biased in a clockwise direction and is adapted to engage a stop lug ll constituting a part of the front carriage plate 41. When the hook 55 is moved downwardly together with the bread carriers, it'will engage a hook-shaped end portion I3 of a substantially vertically extending arm I5 which constitutes one part of an electromagnetically releasable latch comprising a bell crank lever comprising in addition to the vertical arm I5, a substantially horizontally extending arm TI which is pivotally mounted on a pin I9 supported by a pair of lugs 8I which lugs are secured against the under surface of a bracket or, bearing plate 83 which may be secured against the under surface of bottom plate I5 by machine screws 85. An electromagnetic armature core 81 is pivotally mounted on the outer end portion of the substantially horizontally extending arm 11 and is adapted to be energized by an armature coil 89.

Means for controlling the energization of the four toast heating elements 2l comprises a pair of fixed contacts 9I and 93 mounted on a block 95 of electric-insulating material, which is seecured against the upper surface of bottom plate I5. A contact bridging member 91 is insulatedly yieldingly supported by a bracket 99 extending toward the left from the front carriage plate 4'! as seen in Fig. 4 of the drawings, there being a coil spring IIII provided to insure good current conducting engagement between the contact bridging member 91 and the fixed contacts ill and 93. It is to be understood that the position of the fixed contacts 9I and 93 on bottom plate I5 is such that they will be engaged by the contact bridging member 91 when the latter has been moved downwardly with the bread carriers.

Referring now to Figs. 8 and 9 of the drawings, I have there shown a diagram of connections of an electric circuit embodying my invention and comprising particularly an electron tube Hi3 which may be of the grid controlled rectifier type having a plate anode I55, a control grid IIII, an indirectly heated cathode I59, and a heating filament III. The tube is of the type which is electrically non-conducting when a relatively high negative biasing voltage is applied between the control grid It? and the cathode I09, but which becomes conducting when the voltage thus applied has been decreased to a predetermined relatively low value.

The heated filament III is connected to the terminals of a small resistor II3 by means of conductors H5 and Ill. Resistor II3 has such resistance that the filament III is energized to the proper degree when contact bridging member 91 engages contacts SI and 93. Resistor II3 has one terminal connected to a first supply circuit conductor I I9. A second supply circuit conductor I2I is also provided and these two conductors are connected to a connecting plug I23. Supply circuit conductor IZI is connected by a conductor I25 to fixed contact 9i. The other terminal of resistor H3 is connected to one terminal of one of the toast heating elements 2| while the other terminal of this first heating element is connected to one terminal of a second toast heating element, the other terminal of which is connected by a conductor IZ'I to the second fixed contact 93.

Conductor I21 has one of its ends connected not only to fixed contact 93 but also to one terminal of the electromagnetic coil 89 as well as to one terminal of a small condenser I29 which is connected in shunt circuit relatively to the coil 89 so as to reduce chatter since the coil 89 will be traversed by alternating current at the time of termination of a toasting operation. The other terminal of coil 89 is connected by a conductor I3I to the plate anode I55. It will be noted that the indirectly heated cathode I09 is connected to conductor II5.

I provide a half-wave dry-type rectifier I33, one terminal of which is connected to conductor I2I while the other terminal thereof is connected to a small current limiting resistor I35. The ohmic value of the resistance of resistor l35 may be on the order of ohms. The other terminal of resistor I35 is connected by a conductor I3'I to one contact bar I39 of a twin switch bar assembly comprising in addition to the contact bar I39, contact bars I4I, I43 and I45. These four contact bars are adapted to be supported by a block I41 of electric-insulating material which is secured against the upper surface of bottom plate I5 as by a plurality of short machine screws I49. The design construction and adjustment of the spring contact bars I39, I4l, I43, and I45 is such that normally when knob 5'! as well as the bread carriers themselves are in their upper or non-toasting positions, contact bars I39 and MI are in electrical engagement with each other while contact bars I43 and I45 are out of engagement with each other. I provide further a spacing bar I5I, of electric-insulating material, secured to the outer contact bars I39 and I45 which are longer than bars MI and I43. Contact bar I45 has a cam surface I53 secured thereagainst, the right hand surface thereof as seen, for instance, in Fig. 4 of the drawings where it may be engaged by a roller I55 which is rotatably supported as by a bracket I51 which is secured against the rear carriage plate 45 and extends therefrom in a left hand direction as seen in Fig. 4 of the drawings where it can engage the right hand surface of cam plate I53 during the time when an operator moves knob 67 in a downwardly direction. The result of the engagement of roller I55 against cam surface I53 is that first of all disengagement of the two contact arms I39 and MI is eil'ected, after which engagement of contact arm I45 with arm I43 is effected and maintained during a toasting operation. During the upward or return movement of contact bridging member 91 at the termination of a toasting operation, the engagement between contact arms I45 and I43 which continued during the entire period of a toasting cycle, is interrupted after which contact bars I39 and MI will again be i moved into electricalcontacting engagement witharea-see each other as soon as the roller I55 moves out of engagement with cam surface I53.

Contact arm MI is connected by a conductor I58 to the upper terminal of a timing condenser I59," the lower terminal of which is connected to conductor H5, and the capacitance of which is on the order of about five microfarads.

The upper terminal of condenser I59 is also connected by a conductor I5I to contact bar I43. Contact bar I45 is connected by a conductor I53 to one terminal of a current limiting resistor I65, the ohmic resistance of which is on the order of 10,000 ohms and the other terminal of which is connected to control grid I01.

I provide further a timing resistor I61, the lower terminal of which is connected by a conductor I69 to conductor II5. Resistor I51 is provided with a plurality of taps having fixed contact members I1I, I13 and I secured thereto which fixed contacts are adapted to be engaged by a manually-adjustable contact arm I11, which contact arm is connected by a conductor I19 to conductor I63.

Let it now be assumed that an operator has positioned connecting plug I23 in an energized socket having the proper supply circuit voltage. Under these conditions, that is, before he presses downwardly on knob 61, the rectifier I33 is energized through a circuit comprising supply circuit conductor I2I, rectifier I33, resistor I35, conductor I31, engaged contact bars I39 and MI, conductor I58, timing condenser I59, and then through conductor II5 to the other energized supply circuit conductor I I 9. After the operator has placed one or two slices of bread on the carriers and has pressed downwardly on knob 61, the roller I55 will be moved downwardly into engagement with the contact surface of cam I53 whereby disengagement of contact bars I39 and MI is first eilected after which engagement of the normally disengaged contact bars I43 and I45 is effected as is shown in Fig. 9 of the drawings. This interrupts the charging circuit of condenser I59, which may be of a capacitance on the order of 5 microfarads and which is very quickly charged as soon as the connecting plug I23 was inserted in a connecting socket. Fig. 9 is intended to show the positions of the various contact bars I39, MI, I43 and I45 when the toast heating elements 2I are energized as they will be during the toasting cycle.

Let it now be assumed that the manually-adjustable contact arm I11 is in engagement with the fixed contact I13 and that the ohmic re sistance of timing resistor I51 is on the order of 5 megohms when the temperature of the resister is at substantially ordinary room value. Then the timing condenser I59 will begin to discharge through the timing resistor with a resultant decrease in potential across the terminals of the timing condenser until after a period having a length on the order of 2 to 3 minutes, the potential across the terminals of condenser 159 will have been decreased to a value which will cause firing of the tube I53 with a resultant current flow therethrough through a circuit substantially as fO11OWS3- from supply circuit conductor I2I, through conductor I25, throughclosed switch contacts SI and 93, through coil 89, conductor I3I to plate anode I05, to the cathode 455, and then through conductor H5 to the other supply circuit conductor H9. This will cause quick upward movement of the armature core 51 with the result of causing disengagement of hook member .13 from hook 65 and quick upward move- 6 ment of the bread carriage 3! into their u per or non-toasting positions.

As has already been hereinbefore set forth, the upward movement of roller I55 with the bread carriers restores the circuit to the positions of the contact bars I39 and MI, and M3 and I45 as shown in Fig. 8 of the drawings which will cause recharging of the timing condenser I59 to approximately the peak voltage of the supply cir cuit so that the entire toaster structure is ready for a quickly succeeding second operation.

The timing resistor I61 has a negative temperature coefiicient of resistance, that is, its resistance decreases with an increase of temperature of the resistor and the amount of decrease is suitably eiiected so that upon a quickly succeeding toasting operation, the decrease in resistance is such that the discharge of the timing condenser I59 is greater during a given period of time, that is, it will require a shorter length of time to discharge the condenser I59 to that po-. tential which will cause firing of the tube I03 in a period of time such that substantially the same degree of toasting will be effected by the hotter toaster structure, in a manner now well understood. The same comments will hold for any successive toasting operation and with proper correlation of the temperature coefiicient of resistance oi the timing resistor I51 and the characteristics of the timing condenser I59 as well as of the electron tube I53, will result in substantially the same degree of toasting irrespective of temperature variations of the toaster structure.

It was hereinbefore assumed that when arm I11 was in engagement with contact I13 that a medium piece of toast would result and if 1 an operator should desire. say, a light piece of toast, all that would be necessary would bethat he move contact arm I11 into engagement with contact I1I to thereby include a smaller amount of the timing resistor in the discharge circuit of the timing condenser I59. This would result in a decreased length of cycle of a toasting operation with the result that the slice or slices of bread would be toasted to a lesser degree, that is, say, to a light condition. Turning movement of contact arm I11 in a clockwise direction would cause a darker piece of toast to result because of the greater amount of resistance in the discharge circuit of timing condenser I59 whereby a slice or slices of bread would be subject to the radiant heat from the toast heating elements 2| for a longer period of time.

Referring now to Fig. 10 of the drawings, I have there illustrated a modified diagram of connections in which the hereinbefore-mentioned four contact bars are replaced by three contact bars I8I, I83 and I85. Contact bar I has a cam surface I53 secured thereagainst, which cam surface is adapted to be engaged by a roller I55 all as hereinbefore described. I provide further an electric-insulating spacer I81 secured between theupper ends of the longer contact bars I8I and I85. The contact bars ISI, I83 and I85 are mounted as on a block I89 of electric-insulating material having three slots extending therein instead of the four-slot block I41 hereinbefore de-- scribed. Contact bars I 8i and I93 are normally in electric-contacting engagement while contact bars I33 and I85 are normally out of engagement with each other.

A half-Wave dry-type rectifier I33 has one terminal thereof connected to supply circuit conductor I2! while its other end is connected to one terminal of a current limiting resistor I35 having an ohmic resistance on the order of ohms. The other terminal of resistor I35 is connected by a conductor I9I to contact bar I8I while contact bar I83 is connected by a conductor I93 to the upper terminal of timing condenser I59, the lower terminal of which is connected to conductor H5. Contact bar I is connected by a conduotor I to conductor I79, and to the left hand terminal of a current-limiting resistor I65.

All of the other connections are substantially the same as have already been hereinbefore set forth in connection with the diagrams of Figs. 8 and 9.

It is evident that as soon as connecting plug I23 is applied to a connecting socket, that the rectifier I33 will cause energization for charging of the timing condenser I 59 through the closed contact bars I8I and I83- As soon as an operator presses downwardly on knob 61, roller I55 will engage the surface of cam I53 causing disengagement of contact bars I8! and I83 after which contact bars I83 and I35 will be moved into engagement with each other whereby timing condenser I59 will start to discharge through timing resistor I6! with an attendant decrease of potential across its terminals. When the potential across the terminals of condenser I59 has reached a value sufficiently low to cause firing of tube I03, the tube will fire and substantially the same circuit is available for current flow through the tube I93 and coil 89 as also hereinbefore set forth in connection with diagrams shown in Figs. 8 and 9.

Substantially the same comments as hereinbefore made in connection with Figs. 8 and 9 apply also equally well to Fig. 10 as regards the compensation for temperature increase of the toaster structure resulting from quickly successive toastingoperations as well as to meet the demands for different degrees of toasting.

It may be here pointed out that the diagram of connection shown in Figs. 8, 9 and 10 is such as to compensate also for relatively very high supply circuit voltage or relatively very low supply circuit voltage. Thus, if heaters 2| are energized from a circuit, the voltage of which is on the order of 120 volts, the temperature of the radiant heat will be much higher than it is at, say, or even at volts, with the result that the temperature rise of the timing resistor III! which is either subject to radiant heat from the toast heating elements 2I or is subjected to the temperature of a toasting chamber will be increased with an attendant greater decrease of the resistance in the discharge circuit of tube I59 which will result in substantially the same degree of toasting irrespective of variations of the voltage supply circuit.

While I have illustrated two different systems depending upon the use of an alternating current source of supply, I am not limited thereto since if a direct current source of supply only is available, I may omit the rectifier I33 and can obtain substantially the same operation on a direct current source of supply of electric energy.

Various modifications may be made in the system embodying my invention Without departing from the spirit and scope thereof, and all such modifications coming clearly within the scope of the appended claims shall be considered a part of my invention.

I claim as my invention:

1. In an automatic electric toaster the combination with electric toast heating elements, a connecting plug electrically connected to said heating elements and means for starting a toasting operation, of means for timing a toasting 0111-. eration comprising a normally non-conducting electron tube which becomes conducting at a predetermined low potential, a timing condenser, a timing resistor connected in parallel electric circuit with said condenser and said tube and means comprising a normally closed switch for causing said condenser to be fully charged as soon as the connecting plug is connected to a supply circuit, and until said toast heating elements are energized by said starting means.

2. In an automatic electric toaster the combination with electric toast heating elements, a connecting plug electrically connected to said heating elements and means for starting a toasting operation, of means for timing a toasting operation comprising a normally non-conducting electron tube which becomes conducting at a predetermined low potential, a timing condenser, a timingresistor connected in parallel electric circuit with said condenser and said tube and means comprising a normally closed switch for causing said condenser to be fully charged, and to remain its fully charged condition when the connecting plug is connected across a supply circuit and until said toast heating elements are energized by said starting means.

3. In an automatic electric toaster the combination with electric toast heating elements, a connecting plug for said heating elements, a first switch for controlling the energization of said heating elements and means to cause closing of said first switch to start a toasting operation of means fo timing a toasting operation comprising a normally non-conducting tube which becomes conducting at a predetermined low potential, a timing condenser, a timing resistor connectible in parallel electric circuit to said condenser and said tube, means comprising a normally closed second switch for causing said condenser to be fully charged when the connecting plug is connected across a supply circuit and means controlled by said first switch closing means for causing disconnection of said condenser from said charging means when said first switch is closed.

4. In an automatic electric toaster the combination with electric toast heating elements, a connecting plug for said heating elements, a first switch for controlling the energization of said heating elements and means to cause closing of said first switch to start a toasting operation, of

means for timing a toasting operation comprising a normally non-conducting tube which becomes conducting at a predetermined low potential, a timing condenser, a timing resistor connectible in parallel electric circuit to said condenser and said tube, means comprising a normally closed second switch for causing said condenser to be fully charged when the connecting plugis connected across a supply circuit and means controlled by said first switch closing means for causing disconnection of said condenser from said charging means and for causing connection of said condenser in parallel electric circuit relation to said timing resistor and said tube when the heating element switch is closed.

5. In an automatic electric toaster the combination with electric toast heating elements, a connecting plug for said heating elements, a first switch for controlling the energization of said heating elements and means to cause closing of said first switch to start a toasting operation, of means for timing a toasting operation comprising a normally non-conducting tube which becomes conducting at a predetermined low potential, a

timing condenser, a timing resistor connectible in parallel electric circuit to said condenser and said tube, means comprising a normally closed second switch for causing said condenser to be fully charged when the connecting plug is connected across a supply circuit and means controlled by said first switch closing means for causing disconnection of said condenser from said charging means and for causing connection of said condenser in parallel electric circuit relation to said timing resistor and said tube when the heating element switch is closed, said condenser then discharging through said timingresisto until its potential drops to the tube-firing value when the tube becomes conducting and is traversed by an electric current flowing through said connecting plug and means actuable by said current for causing termination of a toasting operation.

6. In an automatic toaster the combination with electric toast heating elements, a connecting plug for said heating elements, a first switch for controlling the energization of said heating elements and normally yieldingly biased into open position, a bread carrier movable into toastingand non-toasting positions relatively to said heating elements and normally yieldingly biased into non-toasting position, means for moving said first switch into closed position and said bread carrier into toasting position and electromagnetically-actuable latch means for holding said first switch in closed position and said bread carrier in toasting position, of means for timing a toasting operation comprising a normally non-conducting electron tube which becomes conducting at a predetermined low potential, a timing condenser, a timing resistor, means for causing charging of said condenser when said connecting plug is connected across a supply circuit, means actuable by said first switch and a carrier moving means for terminating the charging of said condenser and causing connection of said condenser in shunt circuit with said timing resistor and said tube to cause the potential of said condenser to be gradually reduced until it reaches a value at which said tube becomes conducting the current traversing said tube energizing said electromagnetic latch means to cause release thereof and termination of a toasting operation.

7. In an automatic toaster the combination with electric toast heating elements, a connecting plug for said heating elements, a normall open heating element control switch yieldingly biased into open position and movable means for causing closing of said control switch to start a toasting operation, means for timing a toasting operation comprising a normally non-conducting electron tube which becomes conducting when subject to a predetermined low potential, a timing condenser, means for causing said condenser to be fully charged from its charging circuitwhen said connecting plug is connected across an electric supply circuit, a timing resistor means actuable by said control switch closing means during its movement for disconnecting said condenser from its charging circuit and for causing connection of said condenser to said timing resistor and to the tube to cause gradual discharge of said condenser until its potential reaches a value at which said tube becomes conducting and means controlled by the current traversing said tube for terminating a toasting operation.

BROR G. OLVING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,061,011 Vingerhoets Nov. 17, 1936 2,207,946 Sardeson July 16, 1940 2,317,228 Shroyer Apr. 20, 1943 2,364,998 Palmer et a1 Dec. 12, 1944 2,451,508 Olving Oct. 19, 1948 

